Internal gear pump

ABSTRACT

To provide an internal gear pump which is able to stably ensure the sealing property between a resin casing constituting a trochoid accommodating portion and a cover, to omit the seal ring at the portion, and to stabilize the discharging ability. An internal gear pump 1 has a trochoid 4 in which an inner rotor 3 having a plurality of outer teeth is accommodated in an outer rotor 2 having a plurality of inner teeth in a state in which outer teeth mesh with inner teeth and are eccentric, and a casing 5 having a trochoid accommodating recess 5a formed therein, and a cover 6 which closes the recess 5a. The casing 5 is an injection-molded body of a resin composition. The casing 5 and the cover 6 are fixed with bolts. A metallic bush 7 is provided in the bolt fixing hole portion of the casing 5. In the cross-section of the joining portion between the casing 5 and the cover 6, the position of the end surface 7a of the bush 7 is higher than the bush formation surface 5e around the bush of the casing 5 and lower than the sealing surface 5d around the recess of the casing 5, as viewed from the bottom surface 5c of the recess 5a.

TECHNICAL FIELD

The present invention relates to an internal gear pump (a trochoid pump) which feeds a liquid such as oil, water, and chemical liquid.

BACKGROUND ART

The internal gear pump (a trochoid pump) is a pump in which an outer rotor and an inner rotor having a trochoid tooth profile are accommodated in a casing in a sealed state, and with rotation of a drive shaft, the inner rotor and the outer rotor fixed to the drive shaft rotate and act to suck and discharge liquid. In recent years, as a pump of this type, a pump having a casing made of resin has been known as a pump capable of reducing the machining process and capable of being manufactured at low cost (see Patent Literature 1).

The structure of this type of internal gear pump will be described on the basis of FIGS. 4 and 8.

FIG. 4 is a cross-sectional view of a conventional internal gear pump. As illustrated in FIG. 4, a pump 21 mainly includes a trochoid 24 in which an inner rotor 23 having a plurality of outer teeth is accommodated in an annular outer rotor 22 having a plurality of inner teeth. The trochoid 24 is rotatably accommodated in a circular trochoid accommodating recess 25 a formed in a flanged columnar casing 25. A cover 26 which closes the trochoid accommodating recess 25 a is fixed to the casing 25.

The trochoid 24 is configured such that the inner rotor 23 is rotatably accommodated in the outer rotor 22 in a state in which the outer teeth of the inner rotor 23 mesh with the inner teeth of the outer rotor 22 and are eccentric. Volume chambers on a suction side and a discharge side are formed between the partition points on which the respective rotors are in contact with each other, in accordance with the rotation direction of the trochoid 24. A drive shaft 29 rotated by a drive source (not illustrated) passes through and is fixed to the axial center of the inner rotor 23. When the drive shaft 29 rotates and the inner rotor 23 rotates, as the outer teeth mesh with the inner teeth of the outer rotor 22, the outer rotor 22 rotates in the same direction, and liquid is sucked from the suction port into the suction side volume chamber in which the volume increases by the rotation to obtain a negative pressure. The suction side volume chamber changes to a discharge side volume chamber in which the volume decreases and the internal pressure rises by the rotation of the trochoid 24. From this, the sucked liquid is discharged to the discharge port.

The cover 26 is made of a sintered metal, and the casing 25 is an injection-molded body manufactured by injection molding, using a resin composition. A metallic bush 27 is integrated with a bolt fixing hole portion of the casing 25 by composite molding at the time of injection molding, and the casing 25 and the cover 26 are fastened and fixed to the fixing plate 30 of the device main body by a bolt 28 made to pass via the bush 27. The bush 27 is interposed between the casing 25 and the cover 26 to secure the fastening strength at the fastening portion.

A seal ring (O-ring) 31 is assembled in a groove 32 formed on the outer circumference of the recess of the casing 25 on the joining surface (a mating surface) between the casing 25 and the cover 26. Therefore, the trochoid accommodating recess 25 a is sealed, and it is possible to prevent leakage of liquid from the mating surface between the casing 25 and the cover 26. In the internal gear pump, in order to effectively exhibit the pump function, it is important to stably secure the sealing property (sealing property of the trochoid accommodating recess 25 a) on the mating surface between the casing 25 and the cover 26. Hydrogenated nitrile rubber (H-NBR type) or the like is used as the material of the seal ring 31, because the material has heat resistance of about −30° C. to 120° C. and oil resistance, and can be applied to a scroll-type compressor of an air conditioner.

FIG. 8 is a cross-sectional view of another conventional internal gear pump. As illustrated in FIG. 8, a pump 61 mainly includes a trochoid 64 in which an inner rotor 63 having a plurality of outer teeth is accommodated in an annular outer rotor 62 having a plurality of inner teeth. The trochoid 64 is rotatably accommodated in a circular trochoid accommodating recess 65 a formed in a flanged columnar casing 65. A cover 66 that closes the trochoid accommodating recess 65 a is fixed to the casing 65.

The trochoid 64 is configured such that the inner rotor 63 is rotatably accommodated in the outer rotor 62 in a state in which the outer teeth of the inner rotor 63 mesh with the inner teeth of the outer rotor 62 and are eccentric. Volume chambers on a suction side and a discharge side are formed between the partition points on which the respective rotors are in contact with each other, in accordance with the rotation direction of the trochoid 64. A drive shaft 69 rotated by a drive source (not illustrated) passes through and is fixed to the axial center of the inner rotor 63. When the drive shaft 69 rotates and the inner rotor 63 rotates, as the outer teeth mesh with the inner teeth of the outer rotor 62, the outer rotor 62 rotates in the same direction, and liquid is sucked from the suction port into the suction side volume chamber in which the volume increases by the rotation to obtain a negative pressure. The suction side volume chamber changes to a discharge side volume chamber in which the volume decreases and the internal pressure rises by the rotation of the trochoid 64. From this, the sucked liquid is discharged to the discharge port.

The cover 66 is made of a sintered metal, and the casing 65 is an injection-molded body manufactured by injection molding using a resin composition. The casing 65 and the cover 66 are fastened and fixed to the fixing plate 70 of the device main body by a bolt 68. A seal ring 71 is assembled to a groove formed on the outer circumference of the recess of the casing 65 on the joining surface (mating surface) between the casing 65 and the cover 66. Therefore, the trochoid accommodating recess 65 a is sealed, and leakage of liquid from the mating surface between the casing 65 and the cover 66, which is a combination of resin and sintered metal, is prevented.

By using the casing 65 as an injection-molded body (resin molded body), machining is unnecessary and the process is economical. Further, the casing 65 makes sliding contact with the outer rotor 62 and the inner rotor 63 at the bottom surface 65 c and the inner surface 65 b constituting the trochoid accommodating recess 65 a. Since the inner surface 65 b of the trochoid accommodating recess 65 a is an injection-molded body portion of the resin composition, the inner surface 65 b has excellent frictional wear characteristics with respect to the outer rotor 62. The bottom surface 65 c of the trochoid accommodating recess 65 a is constituted by a disc-shaped metal plate 67 integrated with the casing 65 by composite molding. Therefore, there is no problem such as sink marks when the bottom surface 65 c is formed of resin, flatness is excellent, and variation in discharging performance is suppressed.

CITATIONS LIST Patent Literature

Patent Literature 1: JP 2014-51964 A

SUMMARY OF INVENTION Technical Problems

As described above, in the internal gear pump in which the casing of FIG. 4 is made of resin, in order to secure the fastening strength at the fastening portion of the pump, the metallic bush which is composite-molded (insert-molded) with the casing is used. Here, in order to stably hold the fastening force, it is necessary to prevent the resin from being covered on the cover side end surface, which is the joining surface with the bush cover, at the time of molding. For this purpose, for example, it is conceivable that a bush formation surface of the casing around the bush is recessed from the sealing surface (mating surface with the cover) or the bush end surface, and the bush slightly protrudes from the bush formation surface.

However, in the related art, a positional relation between the sealing surface, the bush formation surface, and the bush end surface after molding is not determined, and depending on the protrusion amount of the bush and the molding conditions of the casing, the sealing surface may be lower than the end surface of the bush. In that case, the bush is in contact with the cover because it is a bolt fastening portion, but the sealing surface is not in contact with the cover, and the sealing property at the sealing portion is not secured. In this case, the sealing property is ensured by the seal ring.

When the sealing property is ensured by a seal ring of H-NBR type or the like, the seal ring cannot be used in an atmosphere having a higher temperature than the heat resistant temperature of 120° C. Further, in the pump manufacturing process, a process of assembling the seal ring is required.

The present invention (first aspect described below) has been made to cope with such a problem, and an object thereof is to provide an internal gear pump which is able to stably ensure the sealing property between the resin casing constituting the trochoid accommodating portion and the cover, to omit the seal ring at the portion, and to stabilize the discharging ability.

Further, in the internal gear pumps as described above with reference to FIGS. 4 and 8, the casing is manufactured by injection molding of resin in order to manufacture the pump at low cost. However, the depth dimension and the diameter dimension of the trochoid accommodating portion remain as injection-molded finish, and there are slight variations for each product. In particular, since the depth of the accommodating portion affects the discharge amount, the variation in depth can be a variation in the discharge amount.

The present invention (a second aspect described below) has been made to cope with such a problem, and an object thereof is to provide an internal gear pump capable of reducing variations in the depth of a trochoid accommodating portion among the individual parts, and having stable discharging ability.

Solutions To Problems

According to a first aspect of the present application, there is provided an internal gear pump having a trochoid in which an inner rotor having a plurality of outer teeth is rotatably accommodated inside an outer rotor having a plurality of inner teeth in a state in which the outer teeth mesh with the inner teeth and are eccentric, and an suction side volume chamber configured to suck a liquid, and a discharge side volume chamber configured to discharge the liquid sucked into the suction side volume chamber are formed between the inner teeth and the outer teeth, the internal gear pump including: a casing having a recess which accommodates the trochoid, and a cover which closes the recess of the casing. The casing is an injection-molded body of a resin composition. The casing and the cover are fixed with bolts, a metallic bush is provided in a bolt fixing hole portion of the casing, and a position of an end surface of the bush on the cover side in a cross-section of a joining portion between the casing and the cover is higher than a bush formation surface of the casing around the bush, and is the same as or lower than the sealing surface around the recess of the casing, as seen from a bottom surface of the recess.

The sealing surface may be a surface which is continuous from an inner surface of the recess of the casing, and the sealing surface may come into close contact with the surface of the cover to seal the recess.

A seal ring may not be interposed at a joining portion between the casing and the cover, in the internal gear pump.

An inner surface of the recess of the casing may be made of an injection-molded body of the resin composition, and a bottom surface of the recess may be made of a metal body.

The resin composition may be a resin composition in which a polyphenylene sulfide resin is used as a base resin, and the base resin is blended with at least one selected from a glass fiber, a carbon fiber, and an inorganic filler.

According to a second aspect of the present application, there is provided an internal gear pump having a trochoid in which an inner rotor having a plurality of outer teeth is rotatably accommodated inside an outer rotor having a plurality of inner teeth in a state in which the outer teeth mesh with the inner teeth and are eccentric, and an suction side volume chamber configured to suck a liquid, and a discharge side volume chamber configured to discharge the liquid sucked into the suction side volume chamber are formed between the inner teeth and the outer teeth, the internal gear pump including: a trochoid accommodating portion made of sintered metal configured to accommodate the trochoid, and a casing joined to the outside of the trochoid accommodating portion, in which the casing is an injection-molded body of a resin composition, and the trochoid accommodating portion and the casing are joined such that a part of the casing enters a sintered pore on the outer surface of the trochoid accommodating portion.

The trochoid accommodating portion may include a main body portion having a cylindrical inner surface and a flat plate-like inner bottom surface, and a lid portion which closes an opening portion of the main body portion. Further, the lid portion may be caulked and fixed to the opening portion of the main body portion.

Further, in the configuration in which the trochoid accommodating portion includes the main body portion and the lid portion, the trochoid accommodating portion and the casing maybe joined such that a part of the casing enters the sintered pore of the main body portion and the outer surface of the lid portion in the trochoid accommodation portion.

Advantageous Effects of Invention

The internal gear pump according to the first aspect of the present application has a casing having a trochoid accommodating recess and a cover which closes the recess, and the casing is an injection-molded body of a resin composition. The casing and the cover are fixed with bolts, a metallic bush is provided in a bolt fixing hole portion of the casing, and a position of an end surface of the bush in a cross-section of a joining portion between the casing and the cover is higher than a bush formation surface of the casing around the bush, and is the same as or lower than the sealing surface around the recess of the casing, as seen from a bottom surface of the trochoid accommodating recess. Thus, it is possible to prevent the end surface of the bush from being covered with resin at the time of molding of the casing. Further, regardless of the molding conditions of the casing, the sealing surface preferentially comes in close contact with the cover at the time of fastening the bolt and is always in constant with the cover, the sealing ability of the trochoid accommodating recess can be stably ensured at that portion, and the discharging ability is stabilized.

Further, since the sealing property is ensured as described above, the seal ring conventionally arranged on the outer circumference of the sealing surface can be omitted. Therefore, in the pump manufacturing process, a process of assembling the seal ring is unnecessary, and the assembling is easy. Further, the internal gear pump can be used even in an atmosphere having a higher temperature than 120° C. which is the heat resistant temperature of the H-NBR type 0 ring.

The sealing surface is a surface which is continuous from the inner surface of the trochoid accommodating recess of the casing and comes into close contact with the surface of the cover to seal the recess. Thus, it is possible to prevent the liquid from entering between the cover and the casing from the trochoid accommodating recess.

Since the inner surface of the trochoid accommodating recess of the casing is made of an injection-molded body of a resin composition and the bottom surface of the recess is made of a metal body, it is possible to suppress variations in the discharge performance on the bottom surface, while improving the frictional wear characteristics on the inner surface.

Since the resin composition forming the casing is a resin composition in which a polyphenylene sulfide resin is used as a base resin, and the base resin is blended with at least one selected from a glass fiber, a carbon fiber, and an inorganic filler, oil resistance and chemical resistance are excellent, and a dimensional accuracy is also greatly improved.

An internal gear pump according to a second aspect of the present application includes a trochoid accommodating portion made of a sintered metal configured to accommodate the trochoid, and a casing joined to the outside of the trochoid accommodating portion, in which the casing is an injection-molded body of the resin composition, and the trochoid receiving portion and the casing are joined such that a part of the casing enters the sintered pore on the outer surface of the trochoid accommodating portion. That is, the trochoid accommodating portion is a separate component from the casing, and by performing the composite molding (insert molding) of the casing around the trochoid accommodating portion manufactured in advance, a configuration in which both members are joined is obtained. By manufacturing the entire trochoid accommodating portion as a separate component, it is possible to reduce variations in the depth of the accommodating portion among the individual parts. In addition, the depth itself can be processed with high accuracy. As a result, there is no variation in the discharge amount among the individual parts, and an internal gear pump having a stable discharging ability is obtained.

In a case where the trochoid accommodating portion is formed in the casing as in the related art, it is necessary to process the entire casing in order to suppress the variation in the depth of the accommodating portion. However, by forming only the trochoid accommodating portion as a separate component, there is no need to process the entire casing. The trochoid accommodating portion with the adjusted depth may be composite-molded with the casing, and it is possible to suppress additional processing cost. Furthermore, since the trochoid accommodating portion is made of a sintered metal, it can be easily manufactured, and it is strongly joined to the resin casing due to the anchor effect to the sintered pores at the time of composite molding.

Further, by setting the trochoid accommodating portion as an independent part, it is possible to design the discharge amount only with this part. Therefore, the trochoid accommodating portion can be made into a common component. At the time of molding the casing, only composite molding is performed using this trochoid accommodating portion, and the degree of freedom of design can be expanded.

Since the trochoid accommodating portion includes the main body portion having the cylindrical inner surface and the flat plate-like inner bottom surface and the lid portion for closing the opening portion of the main body portion, the accommodating portion depth can be adjusted only by planar processing of the axial cross-section of the cylinder, and the machining is easy.

Since the lid portion is caulked and fixed to the opening portion of the main body portion, the bolt tightening process as in the related art becomes unnecessary. Further, in the case of fastening the resin body and the metal body with bolts, there is a risk of looseness of the fastening portion, but there is no such risk by fixing the main body portion and the lid portion by caulking.

In addition, the trochoid accommodating portion and the casing are joined such that a part of the casing enters the sintered pores on the outer surface of the main body portion and the lid portion in the trochoid accommodating portion, that is, the casing is formed to cover the lid portion side. Accordingly, it is possible to prevent the lid portion from being detached from the main body portion and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an assembled perspective view illustrating an example of an internal gear pump according to a first aspect of the present application.

FIG. 2 is an axial cross-sectional view and an enlarged view of the internal gear pump of FIG. 1.

FIG. 3 is an axial cross-sectional view and an enlarged view illustrating another example of the internal gear pump of the first aspect of the present application.

FIG. 4 is an axial cross-sectional view of a conventional internal gear pump.

FIG. 5 is an axial cross-sectional view illustrating an example of an internal gear pump according to a second aspect of the present application.

FIG. 6 is an axial cross-sectional view illustrating another example of the internal gear pump according to the second aspect of the present application.

FIG. 7 is an axial cross-sectional view illustrating another example of the internal gear pump according to the second aspect of the present application.

FIG. 8 is an axial cross-sectional view of a conventional internal gear pump.

DESCRIPTION OF EMBODIMENTS

An embodiment of an internal gear pump according to the first aspect of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is an assembled perspective view of an internal gear pump, FIG. 2(a) is an axial cross-sectional view of the internal gear pump, and FIG. 2(b) is an enlarged view of the circumference of the sealing surface of the casing in the internal gear pump. As illustrated in FIG. 1, an internal gear pump 1 includes a trochoid 4 in which an inner rotor 3 is accommodated in an annular outer rotor 2, a casing 5 formed with a recess (trochoid accommodating recess) 5 a which rotatably accommodates the trochoid 4, and a cover 6 that closes the trochoid accommodating recess 5 a of the casing 5. The cover 6 has a shape that substantially conforms to the outer shape of the upper surface of the casing 5 in which the trochoid accommodating recess 5 a opens. As illustrated in FIG. 2(a), the casing 5 and the cover 6 are fastened and fixed to a fixing plate 11 of a device main body with bolts 9. Further, a drive shaft 10 coaxially fixed to the rotation center of the inner rotor 3 is provided. The drive shaft 10 is supported by a bearing (not illustrated) which is press-fitted to the cover 6 or the like.

The number of outer teeth of the inner rotor 3 is smaller by one than the number of inner teeth of the outer rotor 2, and the inner rotor 3 is accommodated in the outer rotor 2 in an eccentric state in which the outer teeth are inscribed in and mesh with the inner teeth. Volume chambers on the suction side and the discharge side are formed between the partition points on which the respective rotors are in contact with each other, in accordance with the rotation direction of the trochoid 4. A suction port communicating with the suction side volume chamber, and a discharge port communicating with the discharge side volume chamber are formed on a bottom surface 5 c of the trochoid accommodating recess 5 a of the casing 5. The suction port communicating with the suction side volume chamber and the discharge port communicating with the discharge side volume chamber may be formed in at least one of the casing 5, the cover 6, and the drive shaft 10.

In the internal gear pump 1, as the trochoid 4 is rotated by the drive shaft 10, liquid is sucked from the suction port into the suction side volume chamber in which the volume increases and a negative pressure is obtained. The suction side volume chamber is changed to a discharge side volume chamber in which the volume decreases and the internal pressure rises by rotation of the trochoid 4, and the sucked liquid is discharged from the discharge side volume chamber to the discharge port. The above-described pump action is continuously performed by the rotation of the trochoid 4, and the liquid is continuously fed. Further, by the liquid sealing effect of enhancing the sealing property of each volume chamber by the sucked liquid, the differential pressure generated between the respective volume chambers increase, and a large pump action is obtained.

The cover 6 is made of metal, and the casing 5 is an injection-molded body of a resin composition. When the casing 5 made of resin is fastened to the device main body with the bolts, there is a risk of looseness of the fastening portion due to creep deformation of the resin. Creep measures can also be taken, by utilizing a predetermined resin composition blended with a reinforcing agent or the like to be described below as a resin material. However, in some cases, it may be brittle and inferior in impact resistance. Therefore, a metallic bush 7 is provided in the bolt fixing hole portion of the casing 5 in order to maintain the fastening strength at the fastening portion. The casing 5 and the cover 6 are fastened and fixed to the fixing plate 11 of the device main body, with bolts 9 which have passed via the bush 7.

The metallic bush 7 has a cylindrical shape having a flange 7 b, and is provided to pass through the flange portion 5 g of the casing 5. The bush 7 can be fixed to the casing 5 by press-fitting, or can be fixed by disposing the bush in the metal mold to be integrated (insert molding) by composite molding at the time of injection molding of the casing 5. In particular, by adopting the insert molding and by utilizing the bush 7 made of sintered metal, the resin enters the surface recess of the sintered body, and the bush 7 and the casing 5 are firmly joined by the anchor effect.

As illustrated in FIG. 2(b), the sealing surface 5 d is a surface which is continuous from the inner surface 5 b of the trochoid accommodating recess 5 a, and is in close contact with the surface of the cover to seal the mating surface between the casing 5 and the cover, thereby sealing the trochoid accommodating recess 5 a. In the casing 5, by providing the surface of the cover side adjacent to and continuous with the inner surface 5 b as the sealing surface 5 d, it is possible to prevent the liquid from entering between the cover and the casing from the trochoid accommodating recess.

The internal gear pump according to the first aspect of the present application is characterized by the positional relation between the sealing surface of the casing and the end surface of the bush after molding. That is, the height position of the end surface 7 a on the cover side of the bush 7 is set to a position which is (1) higher than a bush formation surface 5 e of the casing 5 around the bush, and is (2) lower than the sealing surface 5 d around the recess of the casing 5, as viewed from the bottom surface 5 c, on the basis of the bottom surface 5 c of the trochoid accommodating recess 5 a. This relation is a positional relation after molding of the casing 5.

By the relation of (1), it is possible to prevent the end surface 7 a of the bush 7 from being covered with the resin at the time of the composite molding of the casing 5 and the bush 7. A protrusion amount h₁ of the end surface 7 a of the bush 7 from the bush formation surface 5 e is, for example, 0.01 mm to 0.3 mm. If the end surface 7 a of the bush 7 protrudes even slightly, it is possible to prevent the aforementioned covering of resin.

By the relation of (2), since the sealing surface 5 d is located at a position higher than the end surface 7 a of the bush 7, the sealing surface 5 d preferentially comes into close contact with the cover at the time of bolt fastening. Since the relation is defined as the positional relation after molding, regardless of the molding conditions, the sealing surface 5 d is always in contact with the cover, the sealing property of the trochoid accommodating recess 5 a can be stably ensured, and the discharging ability is also stabilized. Further, since sufficient sealing property can also be ensured on the sealing surface 5 d, a seal ring conventionally disposed on the outer circumference of the sealing surface 5 d can be omitted as illustrated in FIGS. 1 and 2.

Further, the height of the end surface 7 a of the bush 7 and the height of the sealing surface 5 d of the casing 5 may be the same. Also in this case, similarly, it is possible to ensure the sealing property on the sealing surface 5 d. Since the sealing surface 5 d and the cover can be more stably brought into contact with each other, it is preferable to locate the sealing surface 5 d at a position slightly higher than the end surface 7 a. A difference h₂ between the height of the end surface 7 a of the bush 7 and the height of the sealing surface 5 d of the casing 5 is, for example, 0.01 mm to 0.3 mm.

In FIG. 2(a), the casing 5 comes into sliding-contact with the outer rotor 2 and the inner rotor 3 on the bottom surface 5 c and the inner surface 5 b constituting the trochoid accommodating recess 5 a. Since the inner surface 5 b of the trochoid accommodating recess 5 a is an injection-molded body portion of the resin composition, the inner surface 5 b has excellent frictional wear characteristics with respect to the outer rotor 2. Further, the bottom surface 5 c of the trochoid accommodating recess 5 a is constituted by a disk-shaped metal plate 8 integrated with the casing 5 by composite molding. As a result, as compared with the case of forming the bottom surface 5 c with a resin, the flatness is excellent, and variations in the discharging performance can be suppressed. As the metal plate 8, a sintered metal body or a melted metal body (sheet metal pressed article) can be adopted.

Further, by forming the casing 5 as an injection-molded body of the resin composition, a liquid suction nozzle 5 h can be integrally formed with the casing 5 with the resin composition. If necessary, the filter 13 can be fixed to the end portion of the liquid suction nozzle 5 h, which serves as a communication path inlet (liquid suction port) to the suction side volume chamber, by welding or the like. Foreign matter can be prevented from entering the pump by the filter 13. In the internal gear pump according to the first aspect of the present application, the configuration of the trochoid accommodating recess is not limited to the configuration illustrated in FIG. 2, and it may be an injection-molded body of a resin composition including the bottom surface. This makes it possible to form the trochoid accommodating recess, without machining by injection molding, and the process is economical.

Another embodiment of the internal gear pump according to the first aspect of the present invention will be described with reference to FIG. 3. FIG. 3(a) is an axial cross-sectional view of the internal gear pump, and FIG. 3(b) is an enlarged view of the circumference of the sealing surface of the casing in the internal gear pump. As illustrated in FIGS. 3(a) and 3(b), in the internal gear pump 1, an annular groove 5f is provided in a portion which seals the outer circumference of the trochoid accommodating recess 5 a, and a seal ring 12 is assembled to the groove 5 f. Other configurations are the same as those of the internal gear pump illustrated in FIG. 2. As illustrated in FIG. 3(b), the sealing surface 5 d is a surface continuous from the inner surface 5 b of the trochoid accommodating recess 5 a, and comes into close contact with the surface of the cover to primarily seal the trochoid accommodating recess 5 a. The height position of the end surface 7 a of the bush 7 on the cover side is set as a position which is (1) higher than the bush formation surface 5 e of the casing 5 around the bush, and is (2) lower than the sealing surface 5 d around the recess of the casing 5, as viewed from the bottom surface 5 c, on the basis of the bottom surface 5 c of the trochoid accommodating recess 5 a.

In the internal gear pump of FIG. 3, in addition to the sealing structure, the seal ring 12 is assembled to secondarily seal the trochoid accommodating recess 5 a from the seal ring 12. Therefore, the sealing property of the trochoid accommodating recess 5 a can be more stably secured, and the safety factor rises. Also in a case where the seal ring 12 is provided, the protrusion amount of the bush in the above-described sealing structure and the like are the same. That is, also in the embodiment of FIG. 3, the protrusion amount h₁ of the end surface 7 a of the bush 7 from the bush formation surface 5 e, and a difference h₂ between the height of the end surface 7 a of the bush 7 and the height of the sealing surface 5 d of the casing 5 each are, for example, set to 0.01 mm to 0.3 mm.

The material of the seal ring is not particularly limited, and rubber materials, such as hydrogenated nitrile rubber, fluororubber, and acrylic rubber, which conform to the usage and the use environment, may be selected. For example, in a scroll-type compressor of an air conditioner, it is preferable to use a hydrogenated nitrile rubber (H-NBR type) because heat resistance of about −30° C. to 120° C. and oil resistance are required.

The resin composition forming the casing uses injection-moldable synthetic resin as a base resin. As the base resin, for example, thermoplastic polyimide resin, polyether ketone resin, polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS) resin, polyamideimide resin, polyamide (PA) resin, polybutylene terephthalate (PBT) resin, polyethylene terephthalate (PET) resin, polyethylene (PE) resin, polyacetal resin, phenol resin and the like are adopted. Each of these resins may be used alone, or a polymer alloy obtained by mixing two or more of them may be used. Among these heat-resistant resins, it is particularly preferable to use a PPS resin, because the PPS resin is excellent in creep resistance, load resistance, abrasion resistance, chemical resistance and the like of molded body.

Glass fiber, carbon fiber, or inorganic filler, which is effective for high strength, high elasticity, high dimensional accuracy, impartation of wear resistance, and anisotropy removal of injection molding contraction, is preferably used alone or in appropriate combination. In particular, the combined use of glass fiber and inorganic filler is excellent in economy and excellent in frictional wear characteristics in oil.

In the first aspect of the present application, it is particularly preferable to use a resin composition in which a linear-type PPS resin is used as a base resin and glass fiber and glass beads are blended as fillers with the base resin. With this constitution, the oil resistance and chemical resistance are excellent, the toughness is excellent, the warpage of the flange portion is small due to the removal of the anisotropy of the injection molding contraction, and the dimensional accuracy is also greatly improved. In addition to this constitution, by omitting the rubber seal ring as illustrated in FIG. 2, it is possible to suitably use the internal gear pump even in a high-temperature atmosphere exceeding 120° C.

Means for mixing and kneading these various raw materials is not particularly limited, the powder raw materials may be dry-mixed by a Henschel mixer, a ball mixer, a ribbon blender, a Lodige mixer, an Ultra Henschel mixer or the like, and the powder raw materials are melt-kneaded with a melt extruder such as a twin-screw extruder to obtain molding pellets. Further, side feeding may be adopted for injecting the filler, when performing the melt-kneading with a twin-screw extruder or the like. The casing is formed, using this molding pellet, by the injection molding. At the time of molding, a metallic bush is placed in the metal mold and integrated by the composite molding. Further, at the time of molding, the shape of the metal mold and the molding conditions are set such that the bush and the casing satisfy the above-mentioned relations (1) and (2) after molding.

In the internal gear pump of the first aspect of the present application, in addition to the above-mentioned metals (iron, stainless steel, sintered metal, aluminum alloy, or the like), resin (similar to casing) can be used for the cover, and the cover may be a composite-molded body of metal and resin. Sintered metal (iron type, copper iron type, copper type, stainless steel type or the like) is preferably used for the outer rotor and the inner rotor, and iron type is particularly preferable in terms of price. However, in a trochoid pump for pumping water, chemical liquid or the like, a stainless steel type or the like having high rust prevention ability may be adopted.

An embodiment of the internal gear pump according to a second aspect of the present invention will be described with reference to FIG. 5. FIG. 5 is an axial cross-sectional view of the internal gear pump. As illustrated in FIG. 5, the internal gear pump 41 includes a trochoid 44 in which an inner rotor 43 is accommodated in an annular outer rotor 42, a trochoid accommodating portion 46 which rotatably accommodates the trochoid 44, and a casing 45 joined to the outside of the trochoid accommodating portion 46 to support the trochoid accommodating portion 46. The trochoid accommodating portion 46 includes a main body portion 47 having a cylindrical inner surface 47b and a flat plate-like inner bottom surface 47 c, and a lid portion 48 which closes an opening portion 47 a of the main body portion 47. Further, a drive shaft 49 coaxially fixed to the rotation center of the inner rotor 43 is provided. The drive shaft 49 is supported by bearings (not illustrated) provided in the casing 45 or the like. The lid portion 48 and the casing 45 have opening portions at portions through which the drive shaft 49 passes. The internal gear pump 41 is fastened and fixed to a member (not illustrated) of a device main body with bolts via bolt fixing holes 50 formed in the flange 45 b of the casing 45.

The number of outer teeth of the inner rotor 43 is smaller by one than the number of inner teeth of the outer rotor 42, and the inner rotor 43 is accommodated in the outer rotor 42 in an eccentric state in which the outer teeth are inscribed in and mesh with the inner teeth. Volume chambers on the suction side and the discharge side are formed between the partition points on which the respective rotors are in contact with each other, in accordance with the rotation direction of the trochoid 44. On the inner bottom surface 47 c of the main body portion 47 of the trochoid accommodating portion 46 of the casing 45, a suction port communicating with the volume chamber of the suction side and a discharge port communicating with the volume chamber of the discharge side are formed.

In the internal gear pump 41, as the trochoid 44 is rotated by the drive shaft 49, liquid is sucked from the suction port into the suction side volume chamber in which the volume increases and a negative pressure is obtained. The suction side volume chamber is changed to a discharge side volume chamber in which the volume decreases and the internal pressure rises by the rotation of the trochoid 44. The sucked liquid is discharged from the discharge side volume chamber to the discharge port. The above-described pump action is continuously performed by the rotation of the trochoid 44, and the liquid is continuously fed. Further, due to the liquid sealing effect of enhancing the sealing property of each volume chamber by the sucked liquid, the differential pressure generated between the respective volume chambers increases, and a large pump action is obtained.

The trochoid accommodating portion 46 (the main body portion 47 and the lid portion 48) is made of a sintered metal, and the casing 45 is an injection-molded body of a resin composition. The trochoid accommodating portion 46 and the casing 45 are integrally formed (insert-molded) by composite molding, by disposing the trochoid accommodating portion 46 in the mold at the time of the injection molding of the casing 45. In terms of the structure, there is a state in which a part of the resin constituting the casing 45 enters a part of the sintered pores on the outer surface of the trochoid accommodating portion which is a sintered body, and is firmly joined by the anchor effect.

In the configuration illustrated in FIG. 5, a casing 45 is formed to cover not only the main body portion 47 of the trochoid accommodating portion 46 but also the lid portion 48. In order to make this form, at the time of manufacturing, first, after inserting the inner rotor 43 and the outer rotor 42 in combination from the side of the opening portion 47 a into the main body portion 47 of the trochoid accommodating portion 46, the lid portion 48 is closed to form the trochoid accommodating portion 46 including the rotor. By placing the trochoid accommodating portion 46 in the injection molding metal mold to perform the above-described composite molding, the lid portion 48 is covered and the casing 45 can be formed. With this structure, it is possible to prevent the lid portion 48 from detaching from the main body portion 47.

Examples of the sintered metal material that can be used for forming the trochoid accommodating portion 46 include an iron type, a copper iron type, a copper type, a stainless steel type, and the like. Since the price is low and adhesion to the resin casing is excellent, it is preferable to adopt a sintered metal containing iron as the main component (which may contain copper). Further, by adopting a sintered metal containing iron as amain component, higher mechanical strength can be obtained. Further, in the case of containing copper, since copper is inferior in adhesion (adhesiveness) to resin to iron, the content of copper is preferably 10% by weight or less. More preferably, the copper content is 5% by weight or less. In the trochoid pump for feeding water, chemical liquid or the like, it is preferable to adopt a stainless steel type or the like having high rust prevention ability.

It is preferable to use a sintered metal that is not impregnated with oil, as the sintered metal which forms the trochoid accommodating portion 46. Further, when oil is used in the molding or recompression shaping (sizing) process of the sintered metal, it is preferable to use a non-oil-containing sintered metal from which oil is removed by solvent washing or the like. Further, the theoretical density ratio of the sintered metal is preferably 0.7 to 0.9. By setting the theoretical density ratio to 0.7 to 0.9, it is possible to obtain the required denseness for securing the strength of the trochoid accommodating portion, and to secure the surface unevenness (sintered pores) for firmly sticking the resin casing to the trochoid accommodating portion.

Adjustment of the accommodating portion depth in the trochoid accommodating portion 46 can be executed by flattening the axial cross-section of the cylindrical side wall of the main body portion 47 and can be easily adjusted by machining.

Since the casing 45 is an injection-molded body of the resin composition and the discharge amount design can be adjusted only with the trochoid accommodating portion 46, the degree of design freedom of the pump shape and the like is widened. Further, the liquid suction nozzle 45 a can be integrally formed with the casing 45 with the resin composition. If necessary, a filter for preventing mixing of foreign matter may be fixed to the end portion of the liquid suction nozzle 45 a, which serves as a communication path inlet (liquid suction port) to the suction side volume chamber, by welding or the like.

The resin composition forming the casing 45 uses a synthetic resin that can be injection-molded as a base resin. Examples of the base resin include thermoplastic polyimide resin, polyether ketone resin, polyether ether ketone (PEEK) resin, polyphenylene sulfide (PPS) resin, polyamide imide resin, polyamide (PA) resin, polybutylene terephthalate (PBT) resin, polyethylene terephthalate (PET) resin, polyethylene (PE) resin, polyacetal resin, phenol resin and the like. Each of these resins may be used alone, or a polymer alloy obtained by mixing two or more kinds may be used. Among these heat-resistant resins, it is particularly preferable to use a PPS resin because the PPS resin is excellent in creep resistance, load resistance, abrasion resistance, chemical resistance and the like of molded body.

It is preferable to use glass fiber, carbon fiber, or inorganic filler which is effective for high strength, high elasticity, high dimensional accuracy, impartation of wear resistance and removal of anisotropy of injection molding contraction, alone or in combination. In particular, the combined use of glass fiber and inorganic filler is excellent in economy and excellent in frictional wear characteristics in oil.

In the second aspect of the present application, it is particularly preferable to use a resin composition in which a linear-type PPS resin is used as a base resin, and glass fiber and glass beads are blended as fillers with the base resin. With this constitution, the oil resistance and chemical resistance are excellent, the toughness is excellent, the warpage of the flange portion is small due to the removal of the anisotropy of the injection molding contraction, and the dimensional accuracy is greatly improved. In addition to this constitution, since the internal gear pump has an independent trochoid accommodating portion and does not require a rubber seal ring as in the related art, the internal gear pump can be suitably used even in a high-temperature atmosphere exceeding 120° C.

Means for mixing and kneading these various raw materials is not particularly limited, and the powder raw materials may be dry-mixed by a Henschel mixer, a ball mixer, a ribbon blender, a Lodige mixer, an Ultra Henschel mixer or the like, and the powder raw materials may be further melted and mixed by a melt extruder such as a twin-screw extruder or the like to obtain molding pellets. In addition, side feeding may be adopted for charging the fillers when performing the melt-kneading of the filler with the twin-screw extruder or the like. The casing is formed using this molding pellet, by injection molding. At the time of molding, the whole of the trochoid accommodating portion or only the main body portion is arranged in the metal mold and integrated by the composite molding.

In the internal gear pump according to the second aspect of the present application, it is preferable to use a sintered metal (iron type, copper iron type, copper type, stainless steel type, or the like) for the outer rotor and the inner rotor in the same manner as the trochoid accommodating portion.

Another embodiment of the internal gear pump according to the second aspect of the present invention will be described with reference to FIG. 6. FIG. 6 is an axial cross-sectional view of the internal gear pump. As illustrated in FIG. 6, an internal gear pump 41 has a structure in which a lid portion 48 is exposed from a casing 45. The remaining configurations are the same as those of the internal gear pump illustrated in FIG. 5. In the embodiment illustrated in FIG. 6, it is possible to manufacture the internal gear pump by a procedure of inserting each rotor into a main body portion 47, and closing the lid portion 48, after performing the composite molding of the main body portion 47 of a trochoid accommodating portion 46 and the casing 45. Further, as in the case of FIG. 5, after the trochoid accommodating portion 46 including the rotor is assembled, it may be composite-molded with the casing. By caulking and fixing the main body portion 47 and the lid portion 48, a bolt tightening process and the like are unnecessary, and the main body portion 47 and the lid portion 48 can be simply and firmly fixed.

Another embodiment of the internal gear pump according to the second aspect of the present invention will be described with reference to FIG. 7. FIG. 7 is an axial cross-sectional view of the internal gear pump. As illustrated in FIG. 7, the internal gear pump 41 has a structure in which a lid portion 48 and a casing 45 are fastened with bolts 51. Therefore, in a trochoid accommodating portion 46, a main body portion 47 and the lid portion 48 are brought into close contact with each other. The remaining configurations are the same as those of the internal gear pump illustrated in FIG. 5. If necessary, a metallic bush may be interposed in a bolt fixing hole 50 in a flange portion 45 b of the casing 45, and the bolt fastening may be performed through the bush. In the embodiment illustrated in FIG. 7, after performing the composite molding of the main body portion 47 of the trochoid accommodating portion 46 and the casing 45, each rotor is inserted into the main body portion 47. Thereafter, the lid portion 48 is fixed to the casing 45 by a bolt.

As described above with reference to FIGS. 5 to 7, the configuration of the internal gear pump according to the second aspect of the present application is not limited thereto. In any of the embodiments, the trochoid accommodating portion is a separate component from the casing, and by performing the composite-molding of the casing around the trochoid accommodating portion manufactured by precisely machining the accommodating portion depth in advance, a configuration in which both members are joined is obtained. As a result, there is no variation in the discharge amount among the individual parts, and an internal gear pump having a stable discharging ability is obtained.

INDUSTRIAL APPLICABILITY

The internal gear pump according to the first aspect and the second aspect of the present application can be suitably used as an internal gear pump (trochoid pump) for feeding liquid such as oil, water, chemical liquid or the like, and in particular, the internal gear pump can be preferably used as an electric water heater using alternative fluorocarbon, carbon dioxide or the like as a refrigerant, a room air conditioner, and a pump for supplying liquid to sliding parts of a scroll-type compressor for a car air conditioner.

REFERENCE SIGNS LIST

1 Internal gear pump

2 Outer rotor

3 Inner rotor

4 Trochoid

5 Casing

6 Cover

7 Bush

8 Metal plate

9 Bolt

10 Drive shaft

11 Fixing plate of device main body

12 Seal ring

13 Filter

41 Internal gear pump

42 Outer rotor

43 Inner rotor

44 Trochoid

45 Casing

46 Trochoid accommodating portion

47 Main body portion

48 Lid portion

49 Drive shaft

50 Bolt fixing hole

51 Bolt 

1. An internal gear pump having a trochoid in which an inner rotor having a plurality of outer teeth is rotatably accommodated inside an outer rotor having a plurality of inner teeth in a state in which the outer teeth mesh with the inner teeth and are eccentric, and an suction side volume chamber configured to suck a liquid, and a discharge side volume chamber configured to discharge the liquid sucked into the suction side volume chamber are formed between the inner teeth and the outer teeth, the internal gear pump comprising: a casing having a recess which accommodates the trochoid; and a cover which closes the recess of the casing, wherein the casing is an injection-molded body of a resin composition, the casing and the cover are fixed with bolts, a metallic bush is provided in a bolt fixing hole portion of the casing, and a position of an end surface of the bush on the cover side in a cross-section of a joining portion between the casing and the cover is higher than a bush formation surface of the casing around the bush, and is the same as or lower than a sealing surface around the recess of the casing, as seen from a bottom surface of the recess.
 2. The internal gear pump according to claim 1, wherein the sealing surface is a surface which is continuous from an inner surface of the recess of the casing, and the sealing surface comes into close contact with the surface of the cover to seal the recess.
 3. The internal gear pump according to claim 1, wherein a seal ring is not interposed at a joining portion between the casing and the cover.
 4. The internal gear pump according to claim 1, wherein an inner surface of the recess of the casing is made of an injection-molded body of the resin composition, and a bottom surface of the recess is made of a metal body.
 5. The internal gear pump according to claim 1, wherein the resin composition is a resin composition in which a polyphenylene sulfide resin is used as a base resin, and the base resin is blended with at least one selected from a glass fiber, a carbon fiber, and an inorganic filler.
 6. An internal gear pump having a trochoid in which an inner rotor having a plurality of outer teeth is rotatably accommodated inside an outer rotor having a plurality of inner teeth in a state in which the outer teeth mesh with the inner teeth and are eccentric, and an suction side volume chamber configured to suck a liquid, and a discharge side volume chamber configured to discharge the liquid sucked into the suction side volume chamber are formed between the inner teeth and the outer teeth, the internal gear pump comprising: a trochoid accommodating portion made of sintered metal configured to accommodate the trochoid; and a casing joined to the outside of the trochoid accommodating portion, wherein the casing is an injection-molded body of a resin composition, and the trochoid accommodating portion and the casing are joined such that a part of the casing enters a sintered pore on the outer surface of the trochoid accommodating portion.
 7. The internal gear pump according to claim 6, wherein the trochoid accommodating portion includes a main body portion having a cylindrical inner surface and a flat plate-like inner bottom surface, and a lid portion which closes an opening portion of the main body portion.
 8. The internal gear pump according to claim 7, wherein the lid portion is caulked and fixed to the opening portion of the main body portion.
 9. The internal gear pump according to claim 7, wherein the trochoid accommodating portion and the casing are joined such that a part of the casing enters the sintered pore of the main body portion and the outer surface of the lid portion. 